THE ETHMOID BONE. 



141 



Superior conch 

 of the nose 



Cribriform 

 plate 



Anterior ethmoidal 

 groove 



Uncinate process 



jthe orbital surface of the maxilla, the air-sinuses in both situations are completed. 

 ( Posteriorly, the lamina papyracea articulates with the sphenoid, and, at its posterior 

 ! inferior angle for a variable distance, with 

 . the orbital process of the palate bone, both 

 of which serve to close in the air-cells. 

 The medial aspect of the ethmoidal labyrinth 

 displays the convoluted conchae of the nose, 

 usually two in number, though occasion- 

 ally there may be three rarely more. In 

 cases where there are two conchse or ethmo- 

 turbinals 1 they are separated posteriorly 

 by a deep groove. A channel is thus 

 formed in the posterior part of the lateral 

 and upper aspect of the nasal cavity, called 



the superior meatus, which is roofed in bv ^ 



J FIG. 149. SECTION SHOWING THE NASAL ASPECT 



the concha nasalis superior (superior concha), O p THE LEFT LABYRINTH OF THE ETHMOID. 

 whilst its floor is formed by the superior 



surface of the concha nasalis media (middle concha). The posterior ethmoidal cells 

 open into this meatus. In front of the superior meatus, which only grooves the 

 posterior half of this aspect of the bone, the surface is rounded from above 

 downwards and before backwards, and forms the medial wall of the anterior and 

 middle ethmoidal cells. Kunning obliquely from above downwards and backwards 

 over the medial surface of the superior concha, are a number of fine grooves con- 

 tinuous above with the foramina in the cribriform plate ; these are fewer and 

 more scattered in front, do not pass on to the middle concha, and are for the 

 olfactory nerves. 



The middle concha is nearly twice the length of the superior. Its 

 anterior extremity is united for a short distance to the ethmoidal crest on the 



medial side of the frontal 

 process of the maxilla. By 

 its thickened, free convoluted 

 border it overhangs a deep 

 groove which runs along the 

 inferior surface of the ethmoidal 

 labyrinth. This is the middle 

 meatus of the nose. It receives 

 the openings of the middle eth- 

 moidal cells, which project in to the 

 meatus, forming a rounded ele- 

 vation called the ethmoidal bulla. 

 In front of and below the bulla 

 is a groove, the hiatus semilunaris, 



Lacnmal process .P ' ' 



which by articulation above with 

 adjacent bones is converted into 

 a canal, the infundibulum, which 

 ^inferior concha runs upwards and forwards and 

 forms a channel of communication 



Maxillary process Ethmoidal process .,, ,-, f , -, j ,-, 



with the frontal sinus and the 



FIG. 150. SHOWING THE ARTICULATION OF THE INFERIOR . ,, t n n 



CONCHA WITH THE ETHMOID. anterior ethmoidal cells. Curving 



downwards, backwards, and a 



little laterally from the roof of the anterior part of this meatus, in front of 

 the infundibulum, is the processus uncinatus. This bridges across the irregular 

 opening on the medial wall of the maxillary sinus, and articulates inferiorly with 

 the ethmoidal process of the inferior concha. The posterior extremity of the middle 

 concha articulates with the ethmoidal crest on the perpendicular part of the 

 palate bone. 



The lamina cribrosa (cribriform plate) is the horizontal lamina which con- 



Crista galli 



Lamina papyracea 



Alar process 



Perpendicu- 

 lar plate 



Uncinate process 



1 So called to distinguish them from the maxillo-turbinals and naso-turbinals of comparative anatomy. 



